20. c2b3  20... a4b3  21. a2b3 [%c_effect b3;square;b3;type;Mistake;persistent;true] A serious error, mortally weakening the queenside. 21... c7b7 Threatening to capture the pawn on b3, followed by a mating attack. 22. e4f6 A desperate attempt to create a counterattack.